This is nice to know but I would suggest to add an option in parameter, for exemple a check box to select to get a copy of sent invoice and particularely an estimate.
What is "User 1" in 'user1@email.com' => 'user 1', . I putted my e-mail and I left "user 1. It's work but I see not interaction with the parameter 'user 1'. Should I modify it with a name?